1. Field of the Invention
The present invention relates to the use of an extract of Lentinus as well as the pharmaceutical composition that contains it, within the scope of combating cellulite and subcutaneous accumulations of fat.
2. Description of Related Art
The sirtuins are nuclear enzymes belonging to the family of NAD+-dependent deacetylases that occur in practically all organisms, from bacteria to humans.
These proteins, called “silent information regulators”, exert their enzymatic activity on histones, but also on transcription regulators, and thus modulate their activity.
The sirtuins are in fact capable of deacetylating the histones on which the DNA is packed, making it less sensitive to UV and to DNases.
To date, seven sirtuins, called SIRT1 to SIRT7, have been identified in humans. Of these seven sirtuins, there is particular interest in SIRT1, which among other things is involved in skin aging (Dal Farra C. et al., Sirt1, the human homologue to sirt2, is expressed in human skin and in cultured keratinocytes, fibroblasts and HaCaT cells; and its level is closely related to stress and aging, J. Cosmetic Scien., 2006, 57:187-188).
The activity of SIRT-1 deacetylase leads to inhibition of transcription of the genes involved, or “gene silencing”. By this mechanism, SIRT-1 takes part in the regulation of protein p53, a transcription factor involved in the apoptotic cellular pathways, which is acetylated and activated during cellular stress or DNA damage. Thus, SIRT-1 can induce deacetylation of protein p53, i.e. its inactivation, and block its transcription, thus permitting prolongation of cellular longevity (Cheng H L et al. Proc Natl Acad Sci USA. 2003).
All of the bibliographical data clearly indicate that SIRT1 is involved in the ageing process (Porcu M. and Chiarugi A., Trends Pharmacol Sci, 2005; Langley E et al., EMBO J. 2002; H S Ghosh, Current Opinion in Investigational Drugs 2008 9:1095-1102; David Sidransky et al., Cell Cycle 5:17, 2005-2011, 1 Sep. 2006).
Increased expression of SIRT1 in young cells thus contributes, by deacetylation of protein p53 and of histones, to promotion of cellular longevity. However, expression of the protein SIRT1 decreases with age. It has in fact been shown that human fibroblasts aged by successive replicative passages display reduced endogenous expression of the protein SIRT-1 (Michishita et al., Mol Biol Cell. 2005 October; 16(10):4623-35).
In centenarians, the overexpression of certain genes (such as IL10) or of particular proteins such as the sirtuins might explain their longevity.
SIRT1 is therefore regarded as a longevity protein which:                promotes cell survival and participates in the natural DNA defence system by deacetylating the histones on which the DNA is packaged;        inhibits apoptosis by deacetylating the “DNA repair factor” protein Ku70, which permits this protein to sequester in the cytoplasm and inactivate the factor Bax, which is known to promote apoptosis (Brunet A et al., Cell. 1999; 96: 857-68; Jeong J et al., Mol Med. 2007; 39: 8-13);        deacetylates the nuclear protein p53, which is also involved in the induction of apoptosis.        
The protein SIRT1 also acts at the level of the mitochondria, detoxifying the organism by removing free radicals. In fact, a signalling pathway was recently demonstrated involving the cofactor PGC-1, a key protein in biogenesis and mitochondrial function, and SIRT1 whose activation leads to an improvement in the functioning of the mitochondria (Johan Auwerx et al., MEDECINE/SCIENCES 2007; 23; 840-4).
The protein SIRT1 also possesses the capacity to intervene, at cellular level, in the mechanism that controls the accumulation of fat reserves.
Caloric restriction increases, on the one hand, the expression of SIRT1 in a large range of tissues and this alters the balance in favour of cell survival (David A. Sinclair et al., Science 16 Jul. 2004:Vol. 305. No. 5682, pp. 390-392). On the other hand, when the cell is deprived of nourishment, SIRT1 lowers the activity of another molecule, the nuclear receptor PPAR-gamma, which plays a role in the accumulation of fats (Picard F et al. Nature 2004; 429:771-76).
It is now known that SIRT 1 is identified as a mediator of adipogenesis by its action on lipolysis by inhibition of phosphodiesterase-4. Thus, at adipocyte level, SIRT 1 inhibits adipogenesis and increases lipolysis (Qiao L. et al. J. Mol. Chem. 2006 Dec. 29; 281 (52): 39915-24.). As the concentrations of SIRT1 decrease with age in mammals, this might explain why we put on weight as we get older.
The skin is the organ that provides a covering for the entire surface of the body, and is constituted of three superposed, separate compartments: the epidermis (the covering epithelium), the dermis (supporting connective tissue) and the hypodermis. The epidermis is a stratified epithelium that constitutes the external structure of the skin and provides its protective function. The dermis is a supporting tissue that participates in the strength, elasticity and especially the tonicity of the skin and/or of the mucosae. Underneath the dermis there is a layer of adipose tissues: the hypodermis.
The hypodermis is constituted of a layer of white adipose tissue arranged in lobules attached to the lower part of the dermis by rows of collagen fibres and elastic fibres. It is constituted of the large vacuolized cells, the adipocytes, filled almost entirely with triglycerides. These cells can change quickly in volume, during weight loss or weight gain, and can measure from 40 to 120 μm in diameter, which corresponds to a 27-fold change in volume.
The subcutaneous adipose tissue constitutes the body's largest energy reservoir. It is able to store lipids in the form of triglycerides by a process of lipogenesis and then release them in the form of fatty acids and glycerol by a process of lipolysis. It is the equilibrium between these two metabolic pathways that determines adiposity. The body's lipid reserves are constantly being renewed and are closely related to food intake and the energy needs of the body.
If an imbalance develops in the body between the processes of lipogenesis and lipolysis, the volume and the number of adipocytes may increase; this is called adipocyte hypertrophy and hyperplasia. The excessive development of the adipose mass may then be reflected in changes in the skin's appearance, or may even progress to excessive weight of the individual, and possibly obesity.
Cellulite, which is considered to be unsightly, corresponds to hypertrophy of the adipose cells through excess of triglycerides and hyperviscosity of the ground substance (by polymerization of polysaccharides). These changes interfere with cellular exchanges and the mobility of the connective fibres (collagen, elastin and reticulin), which is reflected in water retention, slowing of the venous and lymphatic circulation and loss of flexibility of the skin. The accentuation of adipose tissue is localized, especially in women, at the hips, thighs, buttocks, knees and forearms. The skin takes on a padded and dimpled appearance and at the most advanced stage the “orange-peel” appearance, which is characterized by a succession of depressions caused by excessive stretching of the connective tissue framework and drawing of the epidermis towards the deep tissues.
Nowadays, much research effort is directed at finding an effective means of combating cellulite and excess fat in general. Numerous methods have been employed, for example certain medical-surgical techniques such as lipoplasty, lymphatic drainage, mesotherapy, techniques of ionophoresis etc. However, although these techniques are effective, they are severe and restricting.
There is a need for a gentle, non-invasive means of acting on the mechanisms of formation of excess subcutaneous fat and cellulite.
Action on fatty acid metabolism by cosmetic and pharmaceutical actives so as to prevent the appearance of cellulite, for example by promoting lipolysis or else by inhibiting lipogenesis, i.e. decreasing the formation of triglycerides, has been considered.
However, there is still a need for compounds that make it possible to act on the actual formation and storage of excess subcutaneous fat.